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School of Business Eastern Illinois University The Internet (Week 15, Monday 12/02/2002 and Wednesday 12/04/2002) © Abdou Illia, Fall 2002 Learning Objectives Understand Internet addressing system: – – – – – IP addresses IP address structure Host names DNS Autoconfiguration 2 3 The Internet The Internet is a Worldwide Group of Networks – Not a single network – Routers connect Individual networks Network Router Router 4 The Internet Browser Network Packet Webserver Software Packet Route Router User PC (Host) IP Address=128.150.50.9 Webserver (Host) IP Address=139.67.8.3 Host name=eiu.edu 5 The Internet addressing system Network deliver messages based on network addresses – Host The Internet has two addressing systems for hosts IP addresses. Example: 139.67.8.3 Host names (or domain names or Unique Resource Locators). Example: eiu.edu Host IP Address 6 IP addresses – – – Are really strings of 32 bits (1s and 0s) Example: 10000000101010100001000100001101 Usually represented by four number segments separated by dots: dotted decimal notation Example: 128.171.17.13 Official addresses for hosts 127.18.47.145 127.47.17.47 IP address 32-bits and Dotted Decimal Notation – IP addresses are really strings of 32 bits (1s and 0s) 10000000101010100001000100001101 – To convert this to dotted decimal notation, first, divide them into four bytes (also called octets) 10000000 10101010 00010001 00001101 (Both octets and bytes are collections of eight bits) – Convert each binary (Base 2) octet into decimal (Base 10) 7 8 IP address Position Place Value Bit Decimal (N) (2N) Binary 10100011 = Decimal 163 Note: Starts with 0 7 6 5 4 3 2 1 0 128 64 32 16 8 4 2 1 1 0 1 0 0 0 1 1 128 0 32 0 0 0 2 1 163 9 IP Address structure Each IP Address has two main parts: Network Part Local Part Each Organization is given the Network Part by an IP address Registrar (Ex: www.netsol.com) For Eastern Illinois University, this is 139.67 – All IP Addresses in that Organization’s Network Begin with that Network Part IP Address 139.67 IP Address structure Network Parts can be 8 to 24 bits long – – For Eastern, it is 16 bits long 16 bits is only an example Network Part (8 to 24 bits) Local Part – Total address is 32 bits, so if the network part is 8 bits, the local part is 24 10 11 Assigning Parts Registrar gives organization a network part Organization assigns the local part to its computers internally 139.67.17.13 Registrar 139.67 Firm 139.67.123.130 12 Assigning Parts Most Organizations Have Multiple Segments within the Organizational Network So, usually Local Part is broken in two parts – – a Segment Part to represent each segment Remaining Bits are the Host Part, designating a particular station on that segment Local Part Network Part Segment Part IP Address (32 bits total) Host Part 13 Assigning Parts Registrar gives organization a Network part Organization assigns Segment parts to suborganizations Suborganization assigns Hosts parts to stations 128.171 Registrar 128.171.17.13 Firm Suborganization 128.171.17.13 Host 14 Host name Host Names eui.edu – The other network addressing system on the Internet – Easy to remember microsoft.com eiu.edu Two or more text “labels” separated by dots – 15 Host name Host Names – eiu.edu Like nicknames Not official addresses Each host must have an IP address But only some hosts have host names If you give it a host name, your browser must look up IP address of host Domain Name System (DNS) 16 17 Domain Name System (DNS) User’s computer sends a DNS host the target host’s host name in a DNS Request message DNS host returns the target host’s IP address in DNS Response message eiu.edu Originating Host 139.67.8.3 DNS Host 18 Domain Name System (DNS) Organizations or ISPs have local DNS hosts These hosts must know only local host names and IP addresses For other host names, local DNS host passes request to another DNS host Originating Host Local DNS Host Remote DNS Host 19 Domain Name System (DNS) Remote DNS host passes information back to the local DNS host Local DNS host passes information back to user PC Originating Host Local DNS Host Remote DNS Host Domain Name System (DNS) 20 Autoconfiguration Every computer attached to the Internet is a host – Including desktop PCs Every host must have an IP address Some hosts, such as routers and webservers, get permanent IP addresses – So that they can be found easily 21 Autoconfiguration 22 User PCs do not need permanent IP addresses – They only need to be found within a use session – They usually are given temporary IP addresses each time they use the Internet – They may get a different IP address each time they use the Internet Autoconfiguration 23 Request-Response Cycle – User software requests IP address for the user PC in Autoconfiguration Request message – Autoconfiguration Response message contains temporary IP address to use in current session Autoconfiguration Most popular autoconfiguration protocol is DHCP – – – Dynamic Host Configuration Protocol Built into Windows after Win 3.1 Supplies host with temporary IP address DHCP can give more information too – – – Usually gives IP address of a default gateway (Microsoft terminology for router) Can give IP address of a local DNS host Can give other information 24 Summary Questions 25 1. a) Distinguish between IP address and host name. b) Which is the official address of a host? c) Does a server host need an IP address? d) Does your home PC need an IP address when you are on the Internet? e) Does a server host need a host name? f) Does your home PC need a host name when you are on the Internet? 2. Using the conversion system in slide #8, convert the following IP address to dotted decimal notation: 10101010 11110000 11001100 01010101. (Spaces are included to facilitate reading.) 26 Summary Questions 3. a) What are the three parts in IP addresses? b) What part(s) do border routers look at to determine whether the destination host is within the network or outside of it? 4. a) Who assigns the Network part? b) The Segment part? c) The Host part? 5. a) When do we need DNS? b) What information do you send in a DNS request message? c) What information do you receive in a DNS response message? 4. a) What is autoconfiguration? b) What information do we get back, at a minimum, in an autoconfiguration response message? c) What other information may we get back?